Unreadable game Xbox

Please help.My son uses the xbox not me - I have never been on it so my attempts at solving issues are pathetic.He is up to 28 1st prestige on CoD World at War (He reckons this is impressive).He played it earlier today and has since gone back to it (did not remove the disc) and it says its unreadable. I have polished the disc carefully but it looks unscratched and in mint condition. I read the online help and it looks like the last save might be the problem. He doesnt want to delete as this will mean his hard earned level will be lost. Any ideasIt seems to get to the loading screen but immediately then shows the error.Please help

Re: Unreadable game Xbox

iam pretty sure that online multiplayer stats are saved server side and not hard drive. so he shouldnt worry about losing that prestige.L65 2nd prestige and i anit doing any more for a diffrent badge and an extra custom setup slot after the 4th time round